A thermal imaging camera with a shutter device is known from U.S. Pat. No. 7,484,885 B1.
It is common in thermal imaging cameras to briefly introduce a surface of a homogeneous temperature, which completely interrupts the ray path, into the ray path at regular intervals for image correction. Electromechanical shutter devices, which make possible a change in state between fully interrupted and fully open ray path especially extremely rapidly, are used for this.
A thermal imaging camera with an electromechanical shutter device, with which a shutter flag is pivoted into the ray path in order to make a temperature reference available for image correction, is known from U.S. Pat. No. 7,484,885 B1. The shutter flag is mounted eccentrically directly on the motor shaft of a motor and is rotated to and fro between two end positions correspondingly without transmission with the torque acting on the motor shaft. This leads to high acceleration peaks at the beginning and at the end of the motion and consequently to abrupt start and braking and great vibrations of the shutter flag when the end positions are reached.
Another drawback of the shutter device shown in U.S. Pat. No. 7,484,885 B1 is that pronounced electric current peaks develop in the motor during start-up and braking, which makes use especially difficult in areas with explosion hazard.
Assembly units for such fields of use have, as a rule, the “intrinsically safe” type of protection, i.e., no state leading to the ignition of an explosive gas-air mixture can develop even in case of error. This is usually achieved by limiting the current and voltage to values with which the needed ignition energy is not made available in case of short-circuits or during switching operations.
However, the dynamic characteristic deteriorates and the shutter device becomes slower if the electric power of the drive is limited to the permissible extent. The highly open optical systems employed in thermal imaging cameras require heavy shutters having a relatively large area, so that fast shutter devices, which meet the requirements of explosion protection, can hardly be embodied with this drive concept.